TITLE: GCN CIRCULAR NUMBER: 40129 SUBJECT: IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a) DATE: 25/04/09 14:22:43 GMT FROM: Dmitry Svinkin at Ioffe Institute svinkin@mail.ioffe.ru

D. Svinkin, D. Frederiks, A. Ridnaia, A. Lysenko, and T. Cline on behalf of the Konus-Wind team,

E. Burns on behalf of the IPN,

and

E. Bozzo, C. Ferrigno, and S. Mereghetti on behalf of the INTEGRAL SPI-ACS GRB team,

report:

The long-duration GRB 250321D was detected by Konus-Wind in the waiting mode and INTEGRAL (SPI-ACS) at about 22405 s UT (06:13:25), ~200 s after EP triggered on the fast X-ray transient EP250321a (Hu et al., GCNs 39800, 39833).

We have triangulated it to a Konus-SPI-ACS annulus centered at RA(2000)=176.654 deg (11h 46m 37s) Dec(2000)=+10.352 deg (+10d 21' 08"), whose radius is 11.845 +/- 11.845 deg (3 sigma).

This localization may be improved.

EP250321a is inside the annulus and is consistent with the Konus-Wind ecliptic latitude response, lending support to the association of GRB 250321D and the transient.

A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB250321_T22405/IPN/

The burst time history and spectrum will be given in forthcoming GCN circulars.

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